Also pointed out in the comments is the fact that "fodder corn" or "stalks of Indian corn" (from two of the cited quoted) actually refer to the entire corn plant, i.e. a grass.
However, it does say that the "unhusked ear" broken from the stalk is the most popular feed in the West for fattening cattle (those that are eaten) and "Corn Meal" is favored in the East.
Not really related to your comment, but corn is actually a grass (grasses are a taxonomic group within the plants), so it would be technically accurate (albeit misleading) to say that a cow fed nothing but corn is also "grass fed."
It's true corn is a grass. Actually, all true grains are grasses, I believe, and farmers are allowed to feed a percentage of grain crops and still call their animals "grass fed" if they feed the young sprouts (pre-seed), but the FDA (or USDA?) doesn't allow them to call it grass-fed otherwise.
I wonder what term could be used to replace "grass-fed" that would more specifically define what is meant.